The present application claims priority from Japanese Application No. P2000-252218, filed Aug. 23, 2000, the disclosure of which is hereby incorporated by reference herein.
The present invention relates to a method and device for simultaneously displaying plural images having different formats such as moving pictures, still pictures, and graphics on a display.
With a television receiver, a set top box, etc., which receive digital broadcasts such as a BS (broadcast satellite) digital broadcast, image planes such as moving pictures, still pictures, and graphics can be composed with one another and displayed on a display. Further, there has been proposed a personal computer having a tuner in which the image signals of moving picture planes received through the tuner are composed with the image signals of still picture planes, graphics planes, etc., obtained by the computer and the images thus obtained are displayed on a display.
FIG. 1 is a block diagram showing an example of an image display device as described above in a case where CRT (Cathode Ray Tube) is used as a display.
In the image display device shown in FIG. 1, a compressed moving picture digital video signal is tuned by a tuner 11 and expanded by a decoder 12, and then the moving picture digital video signal thus expanded is input as a moving picture plane from the decoder 12 to a graphics generator 20.
In the graphics generator 20, a background image plane, a still picture plane, a graphics plane such as PNG (Portable Network Graphics) or MNG (Multiple-image Network Graphics) are superimposed on the input moving picture planes in a specified order and at a specified rate, and then the digital image signal after the superimposition is achieved an image plane after superimposition from the graphics generator 20.
For example, as shown in FIG. 2, the moving picture plane MP, the still picture plane SP and the graphics plane GP are superimposed on the background image plane BP in this order, thereby achieving the composite image plane of the above image planes.
The digital video signal after the superimposition from the graphics generator 20 is converted to an analog video signal comprising YUV (luminance signal, color-difference signal of red, color-difference signal of blue) component video signals in a DA (Digital to Analog) converter 31.
The luminance signal Y in the YUV analog video signal is supplied to a high band enhancing circuit 42. In the high band enhancing circuit 42, the high band components of the luminance signal Y are enhanced. The luminance signal thus enhanced in the high band and the color-difference signals UV of red and blue in the YUV analog video signal are converted to an RGB (Red, Green and Blue) analog video signal in a YUV/RGB converter 51, and then the RGB analog video signal thus converted is supplied to an RGB drive circuit 52 to drive CRT 61.
The luminance signal Y of the YUV analog video signal is supplied to a speed modulation circuit 43 in which the luminance signal Y is differentiated to generate a speed modulation signal for modulating the scanning speed of electron beams of CRT 61, and then the speed modulation signal thus generated is supplied to a speed modulation drive circuit 53 to supply speed modulation current to a speed modulation coil 62 provided to CRT 61.
The high band enhancement in the high band enhancement circuit 42 enhances the sharpness of pictures displayed on CRT 61, and also the modulation of the scanning speed of electron beams on the basis of the speed modulation signal from the speed modulation circuit 43 enhances the sharpness of pictures displayed on CRT 61.
In addition to the enhancement of the sharpness by the high band enhancement or the speed modulation as described above, the brightness, contrast, etc., of pictures displayed can be controlled by setting the input/output characteristic of the luminance signal.
In the conventional image display method and device described above, the image quality is controlled in the same level for the moving picture area ME, the still picture area SE and the graphics area GE of the image plane after the superimposition as shown in FIG. 3. That is, in the case of FIG. 1, the sharpness is uniformly enhanced in the moving picture area ME, the still picture area SE and the graphics area GE by the high band enhancement of the high band enhancement circuit 42 and the modulation of the scanning speed of electron beams on the basis of the speed modulation signal from the speed modulation circuit 43.
The enhancement of the sharpness is generally effective to the moving pictures, however, it sometimes has an adverse effect on the still pictures and the graphics pictures. In this case, if the sharpness is enhanced by the high band enhancement or the speed modulation, longitudinal lines and lateral lines look different in width or letters are obscure in some cases. Conversely, if the high band enhancement effect and the speed modulation effect are moderated because more stress is laid on the image quality of the still pictures and the graphics images, the moving pictures would be blurred.
In order to avoid this problem, the image quality of each image (picture) may be individually controlled under the single state of each image plane before these images are arranged on the same pallet, that is, under the state that each of the moving picture plane, the still picture plane and the graphics plane is in the form of an individual digital video signal.
However, with respect to the enhancement of the sharpness by the enhancement of the high band components of the luminance signal, the digital processing has lower degree of freedom in parameters than the analog processing because of the problem in number of taps of a digital filter or the like, and thus it is difficult to arbitrarily control the sharpness. Further, the enhancement of the sharpness by the modulation of the scanning speed of electron beams cannot be implemented for the digital processing.
Therefore, an object of the present invention resides in that when the video signal of a moving picture plane and the video signals of non-moving picture planes such as a still picture plane, and a graphics plane are composed with one another and then the composite image thus achieved is displayed on a display, the optimum image quality can be obtained in each of the moving picture area and the non-moving picture area of the composite image plane, and also high image quality of the overall picture can be implemented.
In order to attain the above object, an image display method according to the present invention includes generating a first video signal of a moving picture plane; generating a second video signal of non-moving picture planes; combining the first video signal and the second video signal to form a composite image plane; displaying the composite image plane on a display; specifying and detecting a moving picture area and a non-moving picture area of the composite image plane; and controlling an image quality of the moving picture area and the non-moving picture area based on a result of the detecting step.
Further, an image display device according to the present invention includes an image plane composing unit operable to combine a video signal of a moving picture plane and video signals of non-moving picture planes to form a composite image plane; a drawing area detecting unit operable to specify and detect a moving picture area and a non-moving picture area of the composite image plane; and an image quality controller operable to control an image quality of the moving picture area and the non-moving picture area on the basis of the detection result.
According to the image display method and the image display device of the present invention, the optimum image quality can be achieved in each of the moving picture area and the non-moving picture area of the composite image plane (the image plane after compositing), and the image quality of the overall image (picture) can be enhanced.